Charge pump regulator circuits may be used to generate an output voltage and current to power a load circuit in an electronic device. There are different types of charge pump regulator circuits, each having different strengths and weaknesses. A common feature of such charge pump regulator circuits is an oscillating signal that is used to generate the output voltage and current. A generally undesirable result of the use of such an oscillating signal is the presence of noise, i.e. ripple or jitter, in the output current and/or voltage of the charge pump regulator circuit, even after passing the output signal through an appropriate filter. Most load circuits, though, can tolerate a certain amount of noise. Nevertheless, various trends in the development of new electronic devices make it a necessity to continually strive for lower and lower levels of noise in such regulator circuits.
A prior art example of a charge pump regulator circuit 100 is shown in FIG. 1. The charge pump regulator circuit 100 generally includes a voltage controlled ring oscillator 101, a high gain buffer 102, a charge pump (a.k.a. voltage multiplier or voltage adder) 103, an RC filter 104 (resistor 105 and capacitor 106), a scaler 107 and an operational amplifier (op-amp) 108. The oscillator 101 generally includes a plurality of inverter stages 109 connected in series output-to-input in a ring. (Some other components or connections are implied, but not shown for simplicity.)
The inverter stages 109 receive a drive voltage (e.g. Vdd) at 110 from the output of the op-amp 108. Under the control of the drive voltage, the signal inverting action of the inverter stages 109 generates an oscillating signal at 111, e.g. the output of one of the inverter stages 109 in the ring. A frequency and amplitude of the oscillating signal at 111 generally depends on a voltage level of the drive voltage.
The oscillating signal at 111 is supplied to an input of the buffer 102. The buffer 102 generates a positive oscillating signal at 112 and a negative oscillating signal at 113. The positive and negative oscillating signals at 112 and 113 generally have the same frequency as the oscillating signal at 111. However, the buffer 102 generally drives an amplitude of the positive and negative oscillating signals at 112 and 113 from rail to rail, i.e. between the same minimum and maximum levels, regardless of the amplitude of the oscillating signal at 111.
The positive and negative oscillating signals at 112 and 113 are supplied to a positive phase input Φ and a negative phase input Φ, respectively, of the charge pump 103. The charge pump 103 generally includes a plurality of series-connected charge pump stages (not shown), which use the positive and negative oscillating signals at 112 and 113 to add voltage to (or subtract from) an initial voltage (not shown) to produce an output current and voltage at 114. The output at 114 of the charge pump 103 is passed through the filter 104 to smooth it out to produce the charge pump regulator circuit output voltage Vout. The output voltage Vout is provided to a load circuit (not shown) of the overall electronic device of which the charge pump regulator circuit 100 is a part.
The output voltage Vout is also provided through the scaler 107 to the op-amp 108 in a feedback loop that controls the current and voltage levels of the output voltage Vout. The scaler 107 produces a scaled voltage at 115 from the output voltage Vout. The scaled voltage is provided to the op-amp 108 along with a reference voltage Vref. The op-amp 108 produces the drive voltage at 110 for the inverter stages 109 based on the scaled voltage at 115 and the reference voltage Vref.
If the scaled voltage at 115 is too large relative to the reference voltage Vref, i.e. the output voltage Vout has increased too much, then the op-amp 108 decreases the drive voltage at 110. When the drive voltage at 110 decreases, the frequency of the oscillating signal at 111 produced by the inverter stages 109 of the oscillator 101 decreases, thereby reducing the frequency of the positive and negative oscillating signals at 112 and 113. When the frequency of the positive and negative oscillating signals at 112 and 113 is reduced, the voltage output at 114 by the charge pump 103 is reduced, thereby reversing the increase in the output voltage Vout. Similarly, if the output voltage Vout decreases too much, then the opposite effect occurs to reverse the decrease. In this manner, the output voltage Vout is generally maintained at about a desired voltage level within an acceptable tolerance or range of ripple or noise.